To give my 2 cents, I tore my hamstring in September and could not start running until the end of december (it was my christmas present). The problem was that I had the Boston Marathon in April. Regardless to say I know exactly how you feel.
You already mentioned that you were going to start swimming, which is great to work on your endurance. Something that helped me that could also start boosting your stregth and endurance is pool running. I swore by this during my recovery. I first started where I could not touch. When I could start taking body weight, I transitioned to running in the shollow end. It will help you work on some of the same muscles and smooth the transition for you to be able to start training on trails.
You can look online for tips/recommendations on how to pool run, etc....
